1. Field of the Invention
The present invention relates to a technique for generating test bitstreams to test bitstream decoders.
2. Description of the Prior Art
Bitstream decoders are generally designed to handle the decoding of bitstreams conforming to a predetermined format. The formats of particular types of bitstreams are typically defined in a fairly systematic manner. For example, the definition may take the form of a syntax defining the format and content of bitstreams generated in accordance with that syntax. This syntax may form part of a protocol relating to such bitstreams. For example, the MPEG-4 ISO-IEC Standard includes syntaxes defining the structure of audio and video bitstreams generated in accordance with the MPEG-4 Standard (see, for example, the ISO-IEC document ISO-IEC 14496-2:1999(E) entitled “Information Technology—Coding of Audio-Visual Objects—Part 2: Visual”, which includes the syntax for video bitstreams conforming to the MPEG-4 Standard). In this example, the syntax is defined in pseudo-C, and a number of tables are provided defining the values that most variables referenced in that syntax can take.
When developing a bitstream decoder for a particular type of bitstream (eg. MPEG-4 video, MPEG-4 audio, etc), it is clearly necessary to perform certain testing of the bitstream decoder to ensure that it is correctly decoding bitstreams that it receives. Generally, this is done by generating a set of test bitstreams aimed at testing the completeness and robustness of the bitstream decoder. The typical prior art approach is to generate a set of test bitstreams on a case by case basis. This process has up to now been largely manual, and requires the developer of the test bitstreams to have both a good understanding of the bitstream standard, and code coverage measurements (i.e. a measurement of how much of the code under test has been exercised by the test data). The basic process is to start with a valid bitstream, and for as long as a component of the decoder has not been tested, to then edit an existing bitstream such that each untested decoder component is then exercised. This process will lead to the generation of a set of test bitstreams, which is deemed complete once each component of the decoder is considered to have been tested.
It is an object of the present invention to provide an improved technique for generating test bitstreams to test a bitstream decoder.